Various methods and apparatus for the reliable recovery of symbol streams from received signals are known. Generally, such methods and apparatus operate by demodulating the received signal, analog-to-digital converting the demodulated signal into an unequalized symbol stream, and equalizing the symbol stream in such a way that the symbols can reliably be mapped to particular points in a so-called symbol constellation. The equalized symbols are then decoded into bit groups, for example, bit pairs, quartets, sextets, octets, and so on, depending upon the complexity of the constellation.
In such methods and apparatus, the equalization process itself is typically adaptive. That is, the unequalized bit stream is input to a device or system which monitors its output symbol stream, and adapts its own transfer function to fit the points of its output symbol stream as closely as possible to points of the symbol constellation. Equalization is frequently conducted with the aid of a so-called Feed Forward Equalizer (FFE) or Feed Forward Filter (FFF) and a Decision Feedback Equalizer (DFE)or Decision Feedback Filter (DFF). In many circumstances, the adaptive equalization process is conducted in at least two phases, or operating modes. In one of these phases, sometimes conducted during initialization of the receiving equipment or when the receiving equipment, for example an HDTV receiver, tunes to another channel, the equalizer employs an algorithm, such as Godard's Constant Modulus Algorithm (CMA). See, for example, D. N. Godard, “Self-Recovering Equalization and Carrier Tracking in Two Dimensional Data Communication Systems”, IEEE Transactions on Communications, Vol. COM-28, pp. 1867-1875, November 1980. Then, after initial convergence, the equalization process enters another phase is which the equalizer transfer function is continuously adapted using another algorithm, such as a decision-directed algorithm, to keep the decoded symbols within a close range of the points on the symbol constellation. The first of these phases is sometimes called a blind phase, the second a decision-directed phase. Methods and apparatus of these types are well known.